1. Field of the Invention
This invention relates in general to the sensing of the linear position of a moveable object or surface, and in particular to sensing devices providing a variable resistance electrical signal output, and actuated by means of a magnet on the moveable object or surface.
2. Description of Related Art
There is a strong demand for a linear position sensor which can serve a dual purpose; one that can measure the position of a moveable object, such as a gate or adjustable weir, and can also be used to measure fluid level. The desired sensor must detect position or level in a continuous and precise manner, must contain no active electronics, and must be sealed from fluid and ambient surroundings.
Related inventions include the DiNola U.S. Pat. No. 3,678,750, the Kubler U.S. Pat. No. 3,976,963, and the Nishida U.S. Pat. No. 4,627,283. These inventions all consist of discrete rather than continuous components, and suffer from poorer resolution than would be available with continuous components. In the Lew U.S. Pat. No. 4,730,491 and U.S. Pat. No. 4,796,472, the resistor is continuous while the switch mechanisms are still discrete. Resolution is greatly improved, but at the cost of considerable complexity. Also, in most embodiments of the Lew invention, the switches are retracted by gravitational force, requiring an upright mounting position for the sensor.
An unpatented sensor manufactured by Hersey Products, Inc. of Spartanburg, S.C. provides the desired features, but is limited in operating temperature range and is relatively difficult to manufacture.